1. Field of the Invention
Present invention is concerned with regulation of access to the transmission capacity in a communication system comprising several nodes and a scheduler interconnected by a transmission medium in which transmitted information sequentially passes the scheduler and nodes, such as in ring systems or recirculating bus systems. In particular, the invention is applicable to systems in which data are transmitted by insertion into time slots, and in which reservation for time slots is made upon previous request by nodes.
2. Description of Related Art
Such systems are known e.g. from European patent application No. 0,388,574 entitled "Method and Apparatus for Distributed Queue Multiple Acces in a Communication System" or European patent application No. 0,393,293 entitled "Method and Apparatus for Cyclic Reservation Multiple Access in a Communication System". The system described in EP-A-0,393,293 is a dual-bus system in which a reserve command is issued for each of several consecutive cycles by a header station, each node requiring access amends a reservation count in this command, and stores in a local queue the number of slots it requested for that cycle. The header station receives the total number of slots requested and checks whether this can be granted. If yes, it sends a confirm command to all nodes and enters the respective slot count (and cycle number) into a global queue. Later, it issues a corresponding number of slots after start of that cycle, and each node knowing how many slots it had reserved can use the respective number of free slots.
If the accumulated request arriving at the header cannot be granted, a general cancel command is issued so that nodes must also cancel the respective reservations. A partial or selective grant is not provided.
In such systems, techniques may be introduced to reuse slots when they have served the communication for which they were reserved, but the traffic situation and location of nodes will give them different opportunities to use this additional transmission capacity.
It would be desirable to have a reservation and grant mechanism which allows a node individual handling, which automatically adapts to the current traffic situation, and which requires a minimum of overhead.